Micromachined cantilevers are the most elementary and successful example of miniaturized sensors. A cantilever, comprising a free-standing beam can often detect changes in the chemical, biological and/or physical properties of the surroundings with sensitivity comparable, if not superior, to much more complicated devices. It is thus not surprising that this simple design is still at the heart of several commercially available instruments, including, but not limited to, an Atomic Force Microscope (AFM). A description of the AFM can be found in G. Binnig, C. F. Quate, Ch. Gerber, Phys. Rev. Lett. 56, 930 (1986), which is included herein by reference.
These instruments rely on the possibility to measure a displacement of the suspended part of the beam perpendicular to its length with up to atomic accuracy, a level of precision that can for instance be achieved by electronic or optical read-out. Methods of measuring the displacement of the suspended part include for instance tunneling probes (G. Binnig, C. F. Quate, Ch. Gerber, Phys. Rev. Lett. 56, 930 (1986)), integrated field-effect transistors (R. G. Beck, et al., Appl. Phys. Lett. 73, 1149 (1998)), capacitive methods (J. Brugger, N. Blanc, Ph. Renaud, N. F. de Rooij, Sens. Actuators, A43, 339 (1994)), piezoelectric or piezoresistive devices (J. Tansock, C. C. Williams, Ultramicroscopy 42-44, 1464 (1992)), optical levers (M. Tortonese, R. C. Barrett, C. F. Quate, Appl. Phys. Lett. 62, 834 (1992), or G. Meyer, N. M. Amer, Appl. Phys. Lett. 53, 1045 (1988)), or optical fiber interferometers (S. Alexander, et al., J. Appl. Phys. 65, 164 (1989), D. Rugar, H. J. Mamin, R. Erlandsson, B. D. Terris, Rev. Sci. Instr., 59, 2337 (1988) or A. D. Drake, D. C. Leiner, Rev. Sci. Instr. 55, 162 (1984)).
Electronic read-outs may be incompatible with the environment where measurements must be performed. Examples of such environments are electrically conductive liquids or extreme temperatures. Furthermore, fabrication of the measurement devices involves cumbersome and expensive processes, an important detail that has limited their commercial and scientific impact. Optical techniques are more widespread than electronic techniques, as their application faces fewer limitations. However, optical techniques generally require an inconvenient, time consuming alignment procedure, which represents a major technical challenge for applications beyond standard experiments.